• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.11C
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• pp.1095-1101
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• 2007

For the cognitive radio (CR) systems sharing the spectrum with narrowband primary devices, this paper presents a fractional bandwidth (FBW) mode utilizing a variable portion of the system band to avoid the interference to or from the primary devices. For the method, the preamble and FBW mode detection algorithm are provided to obtain the FBW mode information during the synchronization. Simulation results in wireless regional area network (WRAN) environments reveal that the FBW mode can be detected reliably without any deterioration of the synchronization performance.

• The Journal of the Acoustical Society of Korea
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• v.32 no.3
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• pp.191-198
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• 2013

In this paper, we designed a wideband Tonpilz transducer, and verified the validity of the design through experiments. The wide frequency bandwidth was achieved by coupling the fundamental longitudinal mode of the transducer with a flapping mode of the head mass. Structure of the Tonpilz transducer was optimized by means of the finite element method and genetic algorithm to achieve the widest fractional bandwidth under design constraints. The optimized structure showed a far wider -6 dB fractional bandwidth of transmitting responses than that of single mode transducers. For verification of the design result, we manufactured a transducer prototype of the designed structure and characterized its performance, which showed good agreement with the design results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2C
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• pp.238-245
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• 2010

For orthogonal frequency division multiplexing (OFDM) systems sharing the spectrum with narrow band primary devices, a fractional bandwidth (FBW) mode has been proposed recently to reduce the interference to the primary users. The FBW mode divides the total OFDM bandwidth into subbands and activates (or deactivates) a subset of the subbands according to the result of spectrum sensing. In this paper, we analyze the detection error probability of FBW mode information which is delivered by the sequence embedded in the preamble and evaluate the performance in wireless regional area network environments. The results show that the detection probability derived analytically estimates the actual value from simulation adequately and that a low detection error probability less than $10^{-3}$ is obtained at a low signal-to-noise power ratio.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.4
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• pp.267-273
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• 2007

A fractional-N frequency synthesizer supports quadruple bands and multiple standards for mobile broadcasting systems. A novel linearized coarse tuned VCO adopting a pseudo-exponential capacitor bank structure is proposed to cover the wide bandwidth of 65%. The proposed technique successfully reduces the variations of KVCO and per-code frequency step by 3.2 and 2.7 times, respectively. For the divider and prescaler circuits, TSPC (true single-phase clock) logic is extensively utilized for high speed operation, low power consumption, and small silicon area. Implemented in $0.18-{\mu}m$ CMOS, the PLL covers $154{\sim}303$ MHz (VHF-III), $462{\sim}911$ MHz (UHF), and $1441{\sim}1887$ MHz (L1, L2) with two VCO's while dissipating 23 mA from 1.8 V supply. The integrated phase noise is 0.598 and 0.812 degree for the integer-N and fractional-N modes, respectively, at 750 MHz output frequency. The in-band noise at 10 kHz offset is -96 dBc/Hz for the integer-N mode and degraded only by 3 dB for the fractional-N mode.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.5
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• pp.583-591
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• 2012

In this paper, using a folded parasitic patch, a hybrid metamaterial antenna having the enhanced bandwidth is presented. To obtain a broad bandwidth of the antenna, a zeroth-order resonance(ZOR) mode of a mushroom antenna and a $TM_{010}$ mode of a conventional patch antenna are combined. By employing an etched rectangular hole and a folded parasitic patch in the conventional patch antenna, a resonance frequency of the $TM_{010}$ mode can be down-shifted toward that of the ZOR mode without changing the size of the antenna. Therefore, the proposed antenna has broad bandwidth which ranges from the ZOR mode to the $TM_{010}$ mode. As a result, a fractional bandwidth of the proposed antenna is measured as 12 % and a radiation efficiency is above 75 % in whole band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.7
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• pp.677-684
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• 2004

This paper presents direct T $M_{01}$-T $E_{11}$ small mode converter using circular waveguide with tilted structure for X-band high power system. It is designed to transmit microwave energy from Relativistic Backward-Wave Oscillator(RBWO) source to hem antenna effectively, with optimized geometry a parameter study The simulated and measured results of return loss, fractional power of each mode, impedance bandwidth and mode pattern are provided.d.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.2 s.117
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• pp.118-125
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• 2007

Harmonic band of bandpass filter(BPF) is suppressed using coupled mushroom structure. Between double positive (DPS) transmission line such as microstrip and double negative(DNG) transmission line such as one dimensional mushroom structure, strong coupling broadly arises in the cross range of dispersion curves of isolated microstrip and mushroom structure because of complex propagation constant in the cross range. Strong coupling inhibits wave propagation, so that this kind of structure can be utilized as bandstop filter(BSF). This BSF utilizes coupled transmission line instead of coupled resonator, resulting in broad bandwidth(>30 %), shan-rejection, and high rejection level. The strong coupling between DPS and DNG transmissionline makes it possible shorten coupling length, resulting in compact size. In this paper, parallel coupled BSF having center frequency of 4 GHz and 3 dB fractional bandwidth of 40 % is designed and utilized to suppressed spurious mode of two bandpass filters.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.3
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• pp.74-78
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• 2011

In this paper, the bandpass filter for ITS system of 5.8 GHz is proposed by using the dual-mode resonator with the radial stub. As alternating the open stub with the radial stub, the size of the dual mode resonator can be reduced about 39.6% and the out-of-band characteristics of the bandpass filter using dual mode resonator can be enhanced from 19.4 dB to 29.1 dB by using the stub of $6.9{\Omega}$ i.e. realized by parallel two radial stubs with $60^{\circ}$ angle. The fabricated bnadpass filter using the dual mode resonator has the center frequency of 5.72 GHz with the fractional bandwidth of 4.1%. Also, the filter has the insertion loss and return loss of 1.79 dB and 19.4 dB, respectively.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.66.2-66.2
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• 2016

KASI and NAOJ are making collaborating efforts to implement faster mapping capability into the new 275-500 GHz Atacama Submillimeter Telescope Experiment focal plane array (FPA). Feed horn antenna is one of critical parts of the FPA. Required fractional bandwidth is almost 60 % while that of traditional conical horn is less than 50 %. Therefore, to achieve this wideband performance, we adopted a horn of which the corrugation depths have a longitudinal profile. A profiled horn has features not only of wide bandwidth but also of shorter length compared to a linear-tapered corrugated horn, and lower cost fabrication with less error can be feasible. In our design process the flare region is represented by a cubic splined curve with several parameters. Parameters of the flare region and each dimension of the throat region are optimized by a differential evolution algorithm to keep >20 dB return loss and >30 dB maximum cross-polarization level over the operation bandwidth. To evaluate RF performance of the horn generated by the optimizer, we used a commercial mode matching software, WASP-NET. Also, Gaussian beam (GB) masks to far fields were applied to give better GB behavior over frequencies. The optimized design shows >23 dB return loss and >33 dB maximum cross-polarization level over the whole band. Gaussicity of the horn is over 96.6 %. The length of the horn is 12.5 mm which is just 57 % of the ALMA band 8 feed horn (21.96 mm).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.5
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• pp.528-536
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• 2010

A monopulse feeder gives the most important impact upon the radiation pattern characteristics of a multi-function radar or a tracking radar which uses the space feed. It is described that the triple-mode type monopulse feeder which possesses the optimum aperture illumination for three monopulse channels is designed and measured in this paper. The measured results show that the designed feeder has not only the characteristics of the optimum aperture illimination in each channel and also very low return loss over the 10 % of fractional bandwidth at X-band. This means that the feeder provides the antenna system with low sidelobe level and high monopulse slope characteristics.